It looks like a good URL shortening site. The design is very professional-looking, and the Google Adsense blends in well. I agree entirely with Porte about the logo. It does not fit in very well with the rest of your site, considering that it is textured. You need a Web 2.0 professional logo to fit with the rest of the site.
As to the script itself, it is very nice that it is AJAX, but it has a few issues. There are two text boxes, and I found it easily to get confused between the two; but
I really like the concept of being able to pick your own tags. That makes it very convenient. This is a nice script, and the short domain goes very well with it.
Last, perhaps you should add some uniqueness to it; since you are building backlinks in the footer, you could do to make them smaller, and I recommend that you add another Adsense box between the two text boxes.
Nice Job.
-Frikkle